5/23/2016  |   15:30 - 15:45   |  309-310

GEOMORPHIC INFLUENCES ON AGE OF CARBON SOURCES TO STREAM DIC AND AQUATIC FOOD WEBS Predicting future effects of climate change on aquatic carbon cycling and food web dynamics at high latitudes requires an understanding of controls on carbon loss and uptake. In SW Alaska, geomorphic characteristics such as watershed slope affect the magnitude of CO2 flux from streams, therefore we predicted that geomorphology similarly influences the carbon sources contributing to stream CO2 emissions and aquatic food webs. We measured carbon isotopes (d13C, d14C) of stream dissolved inorganic carbon (DIC) and invertebrate consumers in a heterogeneous SW Alaska watershed, characterized by a gradient in organic soil accumulation. The isotopic signature of stream DIC (19 sites) varied widely across the landscape (modern to 1800 years bp), reflecting inputs of aged C sources such as peat soil. Rainstorms shifted d14C and d13C of DIC towards values similar to contemporary terrestrial vegetation. d14C of ubiquitous aquatic insects (mayflies) closely tracked stream DIC values, whereas other taxa (caddisflies) reflected modern C sources regardless of watershed characteristics.

Adrianne Smits (Primary Presenter/Author), University of California, Davis, asmits@ucdavis.edu;


Daniel Schindler ( Co-Presenter/Co-Author), University of Washington, deschind@uw.edu;


Gordon Holtgrieve ( Co-Presenter/Co-Author), University of Washington, gholt@uw.edu;


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5/23/2016  |   15:45 - 16:00   |  309-310

INTEGRATING CHEMISTRY, MICROBIOLOGY, AND ECOSYSTEM ECOLOGY TO DISCERN THE NATURE AND FATE OF DISSOLVED ORGANIC MATTER IN STREAMS Aquatic and terrestrial ecosystems are linked through the transfer of energy and materials. Allochthonous organic matter (OM) is central to freshwater ecosystem function, influencing food webs, trophic state, and nutrient availability. Interdisciplinary approaches are necessary to fully understand ecosystem dynamics. We performed a laboratory processing experiment on naturally occurring OM leachates from leaves, grasses, and pine needles. Measures of water chemistry, OM optical and molecular characterization, bacterial abundances, microbial assemblage composition, respiration, and C:N:P were integrated to comprehend the nature and fate of OM. Peak processing occurred after two days, with spikes in bacterial abundances, respiration rates, microbial assemblage shifts, and maximum C utilization. Respiration rates and microbial assemblages differed by OM leachate identity. Leachate lability did not correlate with higher respiration rates, however, C processing efficiency correlated with lability over time. Originally comprised of amino acid-like, labile fluorescent species, stream OM became more recalcitrant after 16 days, indicating stream processing OM humification over time. Our study highlights the importance of interdisciplinary approaches for understanding the processing and fate of OM in aquatic ecosystems.

Juliana D'Andrilli (Primary Presenter/Author), Montana State University, juliana@montana.edu;


James Junker ( Co-Presenter/Co-Author), University of North Texas, james.junker1@gmail.com;


Eric Scholl ( Co-Presenter/Co-Author), U.S. Geological Survey, escholl@usgs.gov;


Heidi Smith ( Co-Presenter/Co-Author), Montana State University, hjsmith12@gmail.com;


Christine Foreman ( Co-Presenter/Co-Author), Montana State University, cforeman@montana.edu;


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5/23/2016  |   16:00 - 16:15   |  309-310

USING THE NOVEL RAZ-RRU METRIC TO QUANTIFY THE INFLUENCE OF BIOFILM COLONIZATION AND SUBSTRATE HETEROGENEITY ON STREAM METABOLISM The resazurin approach (“Raz-Rru”) is a novel method for quantifying heterotrophic respiration in streams, and measures the conversion of resazurin to resorufin in the presence of aerobic bacteria. We examined the dynamics of resazurin conversion (hereafter Kc) as an integrative metric reflecting changes in heterotrophic respiration with varying substrate over a trajectory of biofilm growth/senescence in open-canopy, experimental streams at ND-LEEF. We conducted multiple, short-term additions of resazurin over 5 months in 4 low-nutrient, experimental streams (Q=1.5 L/s, 50m) to quantify the interaction between biofilm colonization, substrate size (1cm pea-gravel vs. 10cm small cobble), and heterogeneity (homogenous 50/50 mix vs. alternating sections) on Kc. In each stream, we found a similar pattern of increasing Kc over the trajectory of biofilm growth, with peak Kc occurring after 3 months (rmANOVA, p<0.001); Kc then decreased with algal senescence. We conducted similar experiments in re-circulating streams to further investigate mechanisms controlling biofilm heterotrophic activity; Kc correlated with both physiochemical (i.e., temperature, dissolved oxygen) and biological characteristics (e.g., chlorophyll a, AFDM). The Kc metric appears sensitive to the interacting drivers of stream ecosystem function.

Brittany Hanrahan (Primary Presenter/Author), USDA Agricultural Research Service, br.hanrahan@gmail.com;


Jennifer L. Tank ( Co-Presenter/Co-Author), University of Notre Dame, tank.1@nd.edu;


Emma Rosi ( Co-Presenter/Co-Author), Cary Institute of Ecosystem Studies, rosie@caryinstitute.org;


Arial Shogren ( Co-Presenter/Co-Author), University of Alabama, ashogren@ua.edu;
Assistant Professor, Department of Biological Sciences, University of Alabama

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5/23/2016  |   16:15 - 16:30   |  309-310

USING PATTERNS OF ECOSYSTEM METABOLISM TO UNDERSTAND A CHANGING, MESOTROPHIC LAKE Maine lakes continue to experience declining water quality, with increasing occurrences of cyanobacterial blooms and seasonal hypoxia. Ecosystem function metrics, such as metabolism, can document changes to lake function on temporal scales ranging from sub-weekly to inter-annual. Here, we use high-frequency open-water metabolism modeling to estimate daily gross primary production (GPP), respiration (R), and net ecosystem production (NEP) for the ice-free season in Great Pond, ME from 2013-2015. Daily estimates of NEP indicate that Great Pond is net autotrophic for much of the ice-free season, and commonly has NEP approaching zero. However, in days following storm events and in the autumn, the lake is more commonly net heterotrophic. Median annual GPP was 0.58 mg O₂ L^-1 day^-1 across years, and median annual R was 0.66 mg O₂ L^-1 day^-1. GPP peaks seasonally in early August, up to 2.70 mg O₂ L^-1 day^-1. Hypolimnetic respiration rates reveal linear patterns of oxygen loss in the bottom waters, leading to hypoxia by August of each year. Examining these patterns result in a deeper understanding of lakes experiencing multiple anthropogenic stressors.

Denise Bruesewitz (Primary Presenter/Author), Colby College, dabruese@colby.edu;


Charles MaCaulay ( Co-Presenter/Co-Author), Colby College, cwmacaul@colby.edu ;


Anne Schechner ( Co-Presenter/Co-Author), Maine Lakes Resource Center, anne.schechner@gmail.com ;


Whitney King ( Co-Presenter/Co-Author), Colby College, dwking@colby.edu;


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5/23/2016  |   16:30 - 16:45   |  309-310

SUMMER STORMS CAUSED LOWER-THAN EXPECTED GROSS PRIMARY PRODUCTION ON THE KLAMATH RIVER DURING THE 2015 DROUGHT YEAR Gross primary production (GPP) and ecosystem respiration (ER) control dissolved oxygen in rivers and they describe resource availability at the base of foodwebs. Our current understanding of controls on river GPP and ER is limited. We calculated daily ecosystem metabolism at 3 sites on the Lower Klamath River from 2007–2015 during May–November. We compared rates and patterns of GPP during the 2015 drought year to GPP during the previous 8 years. Although GPP peaked at 19.7 gO₂m^-2 d^-1 at the mid-river site, the maximum observed value at that site, summer-time means of GPP at all sites were lower than expected based on summer discharge. The 2015 time-series of GPP revealed low daily autocorrelation compared with previous years, driven by summer storms. These storms, which decreased solar radiation and increased water-column turbidity, dramatically decreased reach-scale GPP to near 0 gO₂m^-2 d^-1, while doubling river discharge from a dam-release of a clear-water tributary minimally affected GPP. Antecedent conditions and internal dynamics likely influenced up-river GPP, which was much lower during 2015 than previously observed or expected.

Laurel Genzoli (Primary Presenter/Author), University of Montana, laurel.genzoli@umontana.edu;


Robert O. Hall ( Co-Presenter/Co-Author), Flathead Lake Biological Station, University of Montana, bob.hall@flbs.umt.edu;


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5/23/2016  |   16:45 - 17:00   |  309-310

BALANCING ACCURACY AND COMPUTATION TIME IN STREAM METABOLISM MODELING Ecosystem metabolism is a key driver of carbon exchange and nutrient transformation in streams. Metabolic rates (gross primary production and respiration) can be estimated from continuous dissolved oxygen data, which is widely monitored for water quality reasons. However, metabolism estimates from simple models that treat days separately and only include observation error are often poorly constrained. Complex models that pool information across days and include both process and observation error achieve better accuracy but are slower. Here we compared the computation time and accuracy of these models to two intermediate approaches: (1) a multiphase method that first analyzes days independently and then constrains estimates across days, and (2) a model that pools across days and includes autocorrelated error but does not separate process from observation error. We simulated stream data with ecologically realistic noise, fitted models of varying complexity, and compared the fitted parameters to those used in the simulation. The intermediately complex models were more accurate than simple models and quicker than complex models. These approaches could provide improved estimates of metabolism for spatially or temporally extensive ecological studies.

Alison Appling (Primary Presenter/Author), US Geological Survey, alison.appling@gmail.com;


Robert O. Hall ( Co-Presenter/Co-Author), Flathead Lake Biological Station, University of Montana, bob.hall@flbs.umt.edu;


Charles Yackulic ( Co-Presenter/Co-Author), USGS Southwest Biological Science Center, Grand Canyon Monitoring and Research Center, cyackulic@usgs.gov;


Maite Arroita ( Co-Presenter/Co-Author), University of the Basque Country, maite.arroita@ehu.eus;


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